Electrical filter system



Jan. 19, 1932. G. J. KELLEY 1,842,364

ELECTRICAL FILTER si's'rEM Filed July 20. 1928 2 Sheets-Sheet 1 avwencoz Jan. 19, l932. G. J. KELLEY ELECTRICAL FILTER SYSTEM Filed July 20, 1928 2 Sheets-Sheet 2 @511 abhor/mu Patented Jan. 19, 1932 UNITED ATES. PATENT OFFICE y GERARD J.KELLEY. on NEW YORK, N; Y., ASSIGNQR. BY MEsn assrenmmvrsnro RADIO conronariou WARE s a O AMERIGA, OF NEW YO K, N. Y., a coaroEATIoN or DELA- ELEcTEIc L EILTEE SYSTEM Application filed July 20, 1928. Serial No. 294,109,

The present invention relates generally to electrical filter systems, and more particularly filter systems used in connection wlth the energizing [ofvacuum tube amplifiers 5 from alternating currentor other sources of periodically fluctuating electrical energy.

A. particular object of the invention is the effective filtration of fluctuating electrical energy employed in the energizing of vacuum 19 tube amplifiers connected in cascade arrangements for the purpose of reducing hum 'dis-,

turbances where amplification of such disturbances is involved' A feature of the invention is the employment of apparatus having other useful functions in a composite system in the additional capacity of aiding in the desired effective filtration, an economical and constructional"advantage'of considerable importance.

The present popular demand for radio receivers insists upon an entire elimination-of batteries for energizing the vacuum tube amplifiers used with such receivers with the result that the trendof production is towards a design in which energizing of the tube is accomplished with energy originally derived from the usual commercially availablealterhating current and commutated direct current sources of supply, the designs involving more or less elaborate filter systems and apparatus, the general features of which are well understood and recognized by the personnel of the art. 7

The features and advantages of the present invention are more fully outlined by reference to the figures of the accompanying drawings, like reference characters representing like parts in the several figures so far as possible. 7 i i Fig. 1 illustrates the invention in some of its phases employed in connection with current practicein radio receiver designs.

Fig. 2 illustrates suitable modifications in the arrangement of Fig. lin order to adapt features of the invention to a common modificationof radio receiver design. I

Referring to Flg. 1 the radio IBCGIVGI' is shown to include a three-electrode vacuum tube VT acting as a radio frequency ampli lier, a vacuum tube VT acting as a detector and vacuum tube VT and VT acting as audlo frequency ampl1fiers,@the radio frequency input to the system being indicated as the source S for example, a local oscillator,

an antenna or loop system, or a telegraph line supplying a tunable circuit 1 through a radio frequency transformer RT The radio frequency output of tube vT issupplied to a tunable circuit 2 inthe input circuit of detector tube VT through a radio frequency transformer RT The detector output is supplied to tube V'lgjthrough audio-frequency transformer AT and thence to tube VT, throu h audio fre uenc transformer AT The amplified output is transferred to a loud speaker or other translating device LS through a choke AT and condenser C combination. This choke and condenser combination may be replaced by a two-Winding output transformer, an alternative common in practice, and illustrated in F ig. 2. The operation of the system outlined as a combination radio frequency amplifier, detector and audio frequency amplifier is too well known to require detailed explanation.

The filaments of tubes VT VT and VT;

ar'eindicated as heated by alternating current supplied through transformers ST and 8T though they may be heated in any other suitablemanner. The detector tube VT is indicated 1n a conventional manner as an existing type having a cathode heated by a sep- 7 ners in common use, the polarities of the source being indicated by the and signs shown. Condenser G indicates a part ofthe usual filter system employed in connection with the use of fluctuating energy for; energizing the plate circuits of amplifying tubes.

The usual practice with apparatus currently available employs in the last stage of audio frequency amplification a more or less powerful tube in the position VT. requiring higher potential of plate current than preceding tubes and correspondingly high potential for grid bias. The first audio amplifying tube VT and the radio frequency amplifying tube VT and others if employed, are usually of thesame type employing the same plate current energizing potential and grid bias potential, and are shown so connected in Fig. 1, the potential being less than that of tubeVT The detector tube in position VT generally employs the lowest plate energizing potential, is usually operated with little'or no grid bias potential, and is shown so connected in the figure.

The figure shows the output choke AT of power tube VT'. connected directly to the positive terminal of source S, the usual design providing for the source S producing approximately the desired operating potential for this tube. The primary windings of audio frequency transformer AT and radio frequency transformer RT are shown connected to the positive side of source S through a resistance R which resistance is chosen of such value as to produce a desired reduction of potential in the over-all potential of source S to suit the operating requirements of the particular tubes as amplifiers, and in usual practice may effect a reduction from the neighborhood of 200 or more volts to the neighborhood of from 90 to 150 volts. Condenser C shunted across the reduced potential acts to by-pass signaling currents to the negative side of the source S, is a low impedance to reduce feed-back effects between the tubes, and serves the additional function of further filtering the fluctuating current supplied to the plates of these amplifying tubes. For these reasons this c on denser is chosen of rather large value, such as from 1 to 2 microfarads where the periodic fluctuations of the supply energy are in the neighborhood of cycles per second.

The primary winding of audio frequency transformer AT is connected to the plate side of the output circuit of tube VT through a resistance R of suitable value and the arm of a switch SW placed'upon the lower contact thereof, to further lower the supply potential to suit the operating requirements of tube VT: as a detector. A condenserv C is connected across this reduced potential to the negative side of the source S for the same purposes as condenser C and is also of rather large value for the same reasons givenv in connection with condenser C Since the fluctuating component of the supply energy in the plate circuit of detector tube; VT is twice amplified by tubes V 13 and VT and the audio frequency transformers AT and AT are efficient transfer elements for the frequencies of generally available commercial sources of supply, it is obvious that hum producing currents arising in the detector stage may become quite substantial in magnitude on arrival in the output circuit of tube VT For this reason, it is highly desirable that fluctuating energy supplying tube 'VT be smoothed out to a high degree, and much more so than is required in connection with tube VT and tube VT That is, the filtering should be more perfect in proportion to the amplification that follows the tube in which the fluctuating energizing current is being used. By so connecting the supply to the plate of tube VT that the supply current first passes through primary winding of audio frequency transformer AT there is obtained an additional filtering action cooperating with the filtering action of resistance R and condenser C so that the primary winding of audio frequency transformer AT serves the double function of transferring signal current energy and filtering detector tube supply current energy.

It is pointed out that this proportioning of the filtering from stage to stage in an audio frequency amplifying system in consideration of the degrees of amplification that the hum disturbances are subjected to is of great importance, particularly in an arrangement where advantage is taken of so-called stageto-stage bucking; that is, using the hum disturbances created in one stage to oppose or neutralize the hum disturbances created in other stages, as by properly phasing the windings of the audio frequency transformers to pass the hum from one stage to another in the desired opposing phase. These latter features are not claimed-herein as original with me, being the invention of another, but the'provision I make for using apparatus already a part of the amplifying system for arriving at a high order of filtration for early stages of such a system is of particular value in reducing the cost and complications of arrangements necessary to such systems.

In the event that there is not a substantial difference between the plate potential required for the detector tube and the plate potential required for the first audio tube, the resistance R would be of relatively small value. By reason of its connection it is a shunt to the primary of audio frequency transformer AT so that a small. value of resistance would act to divert alarge amount of signal energy from the transformer, resulting in undue inefficiency. In acase of this kind, or for other reasons, it may be desirable to connect the resistance to the plate side of the second audio frequency tube, using a large resistance R by moving the arm of the switch SW to its upper contact, as in most cases there is a substantial for coupling the loudspeaker.

In some cases to avoidexcessive feed-back effects between tubes interlinked by connection such as described it is desirable to bypass a part'of the potential reducing resistance, afeatureshown in connection with resistance R where the condenser 0' connects an? intermediate point of this resistance to the negative side of source S. In such stituted, these features case it is usually possibleto use less capacity 111 condenserGya's condenser G has a useful filter effect on the detector plate current in the position shown. The feed-back effects referred to may cause so-called motor-boat- 111g if excessive',*or may cause either regenerative amplification to undesirable, degree or loss of amplification by deregeneration depending' upon whether the connections are such as to feed-back in aiding phase or opposing phase, a matter depending uponthe way the windings of the audio frequency transformers are connected in the systeniin the matter of polarity."

Obviously, better filtration of the plate current supplied to the first audio tube V l g could be had by connecting the supply lead to the plate sideof tube VT]; instead of directly to the positive side of source S as shown, and other combinations of connec-' tions to take advantage of my invention are possible, depending upon the particular de signof system;

I have shown resistances R and R connected for obtaining grid bias potentials for the amplifying tubes, these resistances being shunted'by by-pass condensers C and G re- 7 spectively, which features are common practice and require no particular explanation. These resistances are connected to the filaments of thetubes-through potentiometer P and P respectively, also common practice requiring no explanation. ()f. courselother means for obtaining grid bias potentials for operating thetubcs as amplifiers may besubnot being peculiar to my invention.

In Fig. 2 a modification of the amplifying system of Fig; 1 is shown, this being the use ofa so-called push-pull arrangement in the output stage ofthe system comprising the two output tubes VT and VTQ. arrangement'I have provided'a resistance R in shunt to the primary of output transformer AT and connected the supply lead to the plate circuit of detector tube VT to the approximate midpoint of this resistance through a switch SW, the arm of which is In this placednponthe upper contact thereof, this in order to maintain the required balance in the push-pull system. This resistance should vadditional resistance R in series withthe supply circuit, but this may be eliminated and all of the resistance needed for reducing the detector plate circuit potential tothe required value may be included in the resistance element R Obviously the plate current supply for detector tube 'VT is subjected to the filtration effect of the primary winding of output transformer ATs, as well as the filtration effect of resistance R resistance R if used and condenser C The detector tube may have its plate current supply derived from a connection to the plate side of tube VT by movement of the arm of switch SW to the'lower contact thereof, as in the case of Fig. 1, and the tube VT may have its plate current supply derived fromthe output side of the push-pull tubes by way of resistance R by shifting the arm of switch SW to its lower contact, or other modification made to take advantage of the benefits of my invention. v

I -haveshown the filament system of tubes VT and VT connected to the approximatemid-point of the secondary winding of audio frequency transformer AT through a resistance R which maybe shunted by an audio frequency signal current by-passing condenser C and the plates of these tubes connected to the ositive side of the source S through a choke H, this being one procedure for breaking up a tendency on the part of a push-pull connection such as shown from oscillating by reason of feed-back effects inherent to a push-pull connection.

For energizing the plate circuit of amplifying tube VT I have shown a connection from the primary winding of audio frequency transformer AT by way of resistance R; and the switch SW", vhen the arm thereof is moved to its upper contact to the positive side of source S through choke coil CH, this in order to employ the filtering action of this choke if needed in connection with the action of tube VT in the system, thus giving to this choke an additional function. As before the resistance R provides for reducing the potential the desired amount to satisfy theopera-ting requirements of tube VT and the condenser O actsboth as a by-pass condenser for signal currents and an aid to filtering. i s i a I have found that by using the elements pointed out by meinvarious ways as aids to filtering I have been able to make substantial reductions in hum produced when energizing such systems as I have described with fluctuating energy derived from the usual 60 cycle alternating current commercial sources of supply, employing the usual rectifying and filtering devices for converting the raw alternating current into pulsating unidirectional current. I

\Vhile I have particularly described my invention in connection with radio receiving apparatus of popular form, no limitations are intended by reason of such selection, the invention being one of general application.

laying fully described my invention I claim: 7

1. In a system for the successive amplification of alternating current, the combination of a'plurality of multi-electrode electron dischargetubes connected in cascade, impedance signal-transfer means in the output circuits of said tubes, a common source of fluctuating uni-directional current for energizing the anodes of said tubes, and a filter-effective combination of impedances associated with at least two tubes of the system, said combination including as filter-effective elements the impedance-transfer elements in Series connection for the transmission with filter effect therethrough of the anode current for a preceding tube from the outputcircuit of a succeeding tube. I

2. In a system for the successive amplification of alternating current, the combination of a. plurality of multi-electrode electron discharge tubes connected in cascade, impedance signal-transfer means in the output circuits'of said tubes, a common source of fluctuating uni-directional current for energizing the anodes of said tubes, and a filter-effective combination of impedances associated with at least two tubes of the system, said combination including as filter-effective elements the impedance transfer elements in series connection for the transmission with filter effect therethrough of the anode current for a preceding tube from the output circuit of a succeeding tube and an additional filter-effective element comprising a condenser connected at one side to the negative side of said common source, and at the other side between said series connected transfer elements.

3.- In a system for the successive amplification of audio frequency current the combinationof a plurality of three electrode vacuum tubes, audio frequency transformers linking said tubes in cascade relation, an output transformer, a common source of fluctuating unidirectional current and connections for energizing the output electrodes of said tubes, connections whereby the energizing current is positively supplied to the output electrode of a preceding tube after passing through the primary winding of the transformer in the output circuit of a succeeding tube, and a condenser of low impedance to audio frequency current linking said connection to the negative side of said source.

4. In a system for the successive amplifical tion of alternating currents the combination ofaplurality of three electrode vacuum tubes, impedance means linking said tubes in cascade relation, an output impedance means within the output circuit of the last tube of said cascade a common source of fluctuating uni-directional current and connections for energizing the output electrodes of said tubes,

and means for supplying the output electrode of a preceding tube with positive current of substantially lesser potential than the potential of said source and a higher order of filtration than had in the current supplied to succeeding tubes comprising a circuit including an energy consuming device connected to the output electrode of said preceding tube and to the positive'side of said source through the impedance means in the output circuit of a succeeding tube, and a condenser linking the positive side of said energy consuming device to the negative side of said source.

5. In a system for receiving and amplifying high frequency modulated currents including a three electrode vacuum tube for detection followed by one or more tubes, including an output tube for audio frequency amplification, impedance means in the output circuits of said tubes for transferring audio frequency current energy from one tube to the next, an output impedance means within the output circuit of said output tube, a common source of fluctating uni-directional current for energizing the output electrodes of said tubes, a connection for positively energizing the output electrode of said detector tube including means therein for reducing the potential of said source, said connection having included therein the impedance means in the output circuit of one of said audio frequency amplifying tubes, and a condenser linking the output electrode of said detector tube to the negative side of said source.

6. In a system for the successive amplification of alternating currents the combination of a plurality of three electrode vacuum tubes, audio frequency impedance means linking said tubes for cascade amplification, two of said tubes being connected in push-pull relation as a single stage of amplification and preceded by one or more tubes in series relation to saidpush-pull stage, an output impedance means within the output circuits of said tubes arranged in push-pull relation, a common source of fluctuating uni-directional current and connections for energizing the output electrodes of said tubes, a resistance connecting the output electrodes of the tubes of said push-pull stage, a connection to the output electrodeof a preceding tube from an approximate midpoint of said resistance, and a condenser linking said connection to the negative side of said source.

7. In a system for the successive amplification of alternating current the combination of a plurality of three electrode vacuum tubes including an output tube, inductive impedance means in the output circuits of said tubes for transferrlng energy of said currents from one tube to another, an output impedance means within the output circuit of said output tube, a common source of fluctuating unidirectional current and connections for energizing the output electrodes of sald tubes,

one of said connections leading to the output electrode of a preceding tube by way of one of said inductive impedance means in the output circuit of a succeeding tubepa resistance in said connection, a condenser linking an intermediate point of said resistance to the negative side of said source, and a second condenser linking the output electrode of said preceding tube to the negative side of said source. a

In testimony whereof I aflix m signature.

GERARD J. ELLEY. .1 

